mpv drops frames with growing number of maximized windows behind mpv

gnome-shell-3.36.3-3.fc32.x86_64 mutter-3.36.3-2.fc32.x86_64 mpv-0.32.0-3.fc32.x86_64 mesa-dri-drivers-20.0.7-1.fc32.x86_64

Problem exists in Fedora 32 on Intel gen3 chipset:

00:02.0 VGA compatible controller: Intel Corporation 82G33/G31 Express Integrated Graphics Controller (rev 10) (prog-if 00 [VGA controller])
	Subsystem: Foxconn International, Inc. Device 0ded
	Flags: bus master, fast devsel, latency 0, IRQ 16
	Memory at fdf00000 (32-bit, non-prefetchable) [size=512K]
	I/O ports at ff00 [size=8]
	Memory at d0000000 (32-bit, prefetchable) [size=256M]
	Memory at fda00000 (32-bit, non-prefetchable) [size=1M]
	Expansion ROM at 000c0000 [virtual] [disabled] [size=128K]
	Capabilities: <access denied>
	Kernel driver in use: i915
	Kernel modules: i915

Gnome Shell/mutter starts up using OpenGL-ES 2.0 fallback.

All playback tests were made with "mpv --opengl-es=yes --framedrop=decoder+vo" and with a 1440x1080 video on a 1920x1200 VGA video output.

Problem: mpv playback runs without any frame drops when only mpv is shown onscreen. However, if there are maximized windows behind the mpv window, the playback starts dropping frames, and the video becomes choppy. With one maximized window, the framedrop may not happen, but it becomes more severe the more maximized windows are behind mpv.

The framedrop remains even if the mpv window is made fullscreen with the "f" key, even if the ordinary maximized windows are not visible at all.

Minimized windows, or windows in other desktop areas, no matter their number, appear to have no effect on mpv framedrop. Non-maximized windows appear to have little to no effect either.

This looks to be a mutter issue and not a mpv issue because the performance problem is dependent on the window layout. Specifically, the more maximized windows in the same desktop area as mpv, the choppier the video becomes.